The invention relates to a non-contacting position measuring system having a sensor comprising a measuring coil which can be energized with alternating current, where the measuring coil comprises at least two voltage taps, with an electrically and/or magnetically conductive object to be measured which is assigned to the sensor, and with an evaluation circuit, where the sensor and the object to be measured can be displaced relative to one another in the longitudinal direction of the measuring coil.
Non-contacting position-measuring systems have been known in practice for years in the most varied embodiments. In particular, non-contacting position measuring systems with at least one sensor comprising a measuring coil are known, i.e., position measuring systems which operate either on the basis of eddy current or inductively.
Known arrangements for inductive position measurement operate, for example, according to the LVDT (linear variable differential transformer) principle and comprise one primary coil and two secondary coils, where the primary coils are supplied by oscillator electronics with an alternating current of constant frequency. A ferromagnetic core is moved without contact between the coils encapsulated in a housing. Depending on the position of the magnetic core, alternating voltages are induced in the two secondary coils. A displacement of the magnetic core causes a higher voltage in one secondary coil and a lower voltage in the other secondary coil, where the difference of two secondary voltages is proportional to the displacement of the core. It is problematic in this case that the actual object to be measured, whose motion is intended to be detected, must be mechanically connected to the magnetic core so that it picks up the motions to be measured. The connection can, for example, be realized by welding or via a thread. Both variants are mechanically extremely complicated.
From U.S. Pat. No. 5,629,619 an eddy current sensor is known in which a measuring coil has also already been provided with several voltage taps. The partial impedance of the measuring coil between two voltage taps is affected, depending on the position of the ring, by a ring engaging around the coil housing with spacing. With the aid of an evaluation circuit, the position of the ring relative to the voltage taps can be determined. In so doing, there is also the disadvantage that the object actually to be detected must be connected to the ring in a mechanically complicated manner.
The object of the present invention is to develop and extend a position-measuring system operating without contact and of the type stated in the introduction in such a manner that the object to be measured can be defined as a simple machine component.